1. Field of the Invention
The present invention relates to a radiation detector, a radiation imaging system, a radiation detecting method, a radiation imaging method, a computer readable storage medium, and a computer program, particularly suitable for electronically imaging a radiation image of radioactive rays such as X-rays transmitted through a human body or the like.
2. Description of the Related Art
As a conventional method of converting one type of radioactive rays, X-rays, into electric signals and obtaining an X-ray image, a combination of an image intensifier (I.I.) for converting X-rays into light, a television camera and a television is used (I.I.xe2x80x94TV system).
In the I.I.xe2x80x94TV system, the size of an X-ray input plane of an image intensifier is an imaging size. Some system has the size of about 16 inches. An X-ray image converted into light is once focused in an image intensifier output unit, and this output image is taken with a television camera via an optical system to output it as an electrical image. With this system, an X-ray image can be observed in real time. Documents describing such techniques are disclosed, for example, in Japanese Patent Application Laid-open No. 9-276265.
A semiconductor radiation detector has been paid attention as a high speed radiation detector for outputting an image in real time. With this semiconductor radiation detector, there is a problem of dark current noises. Dark current by re-combination at a trap level has been analyzed to date by the Schocklyxe2x80x94Read method.
As the documents describing such techniques, for example, the paper is known which is described in Nuclear Instruments and Methods in Physics Research issued in 1999, A Vol. 434, pp. 44 to 56.
Conventional systems described above are, however, associated with an insufficient resolution which is required to be improved in some degree. As compared with film imaging, the imaging system becomes large so that the installation place is limited and transport of the system is limited. There are still many points to be improved.
For dark current of a semiconductor radiation detector, if a trap cross sectional area of electrons or holes at a trap level is small, analysis for determining specifications cannot be made.
Under the above-described problems, a first feature of the invention is to reliably and correctly detect and image incident radiation.
A second feature of the invention is to detect and image incident radiation with excellent sensitivity characteristics.
The invention provides at least one of the two features.
According to a first aspect of the present invention, there is provided a radiation detector including a radiation detecting element having: a charge emitting layer for converting an incident radioactive ray into an electric charge and emitting the converted charge; a semiconductor layer of a first conductivity type; and a semiconductor layer of a second conductivity type opposite to the first conductivity type, wherein at least the charge emitting layer is sandwiched between the first conductivity type semiconductor layer and second conductivity type semiconductor layer, the radiation detector comprising bias applying means for applying an electric field to the charge emitting layer, the electric field having an intensity satisfying a lower limit of a specification value of a carrier capturing efficiency and an upper limit of a specification value of a dark current density.